The present invention relates to the use of organic light emitting diodes for area illumination and more particularly to area illumination light sources having a plurality of segments.
Solid-state lighting devices made of light emitting diodes are increasingly useful for applications requiring robustness and long-life. For example, solid-state LEDs are found today in automotive applications. These devices are typically formed by combining multiple, small LED devices providing a point light source into a single module together with glass lenses suitably designed to control the light as is desired for a particular application; see for example WO99/57945, published Nov. 11, 1999. These multiple devices are expensive and complex to manufacture and integrate into single area illumination devices. Moreover, LED devices provide point sources of light, a plurality of which are employed for area illumination.
Organic light emitting diodes (OLEDs) are manufactured by depositing organic semiconductor materials between electrodes on a substrate. This process enables the creation of light sources having extended surface area on a single substrate. The prior art describes the use of electro-luminescent materials as adjuncts to conventional lighting; for example, U.S. Pat. No. 6,168,282, issued Jan. 2, 2001 to Chien. In this case, because of the limited light output from the electro-luminescent material, it is not useful for primary lighting.
EP1120838A2, published Aug. 1, 2001 describes a method for mounting multiple organic light emitting devices on a mounting substrate to create a light source. However, this approach of mounting multiple light sources on a substrate increases the complexity and hence the manufacturing costs of the area illumination light source.
In many lighting applications, it is desirable to have a variety of illumination levels and colors. For example, dimmer switches are well known in conventional lighting to provide variable lighting levels between off and full brightness. It is also desirable to have lighting systems that do not fail catastrophically but instead degrade gracefully. Conventional incandescent light bulbs tend to burn out completely when they fail, providing no light rather than reduced light. In other cases it is useful to have a variety of illumination colors. Since the color of outdoor light changes somewhat from dawn to dusk, it is useful to have a lighting system that can complement or mimic the color of outdoor lighting or provide lighting at a variety of color temperatures. Moreover, there are occasions when specific color temperatures are desired for illumination or when, for decorative or entertainment effect, different colors of illumination light are desired.
There is a need therefore for an improved, solid-state flat-panel area illumination device that avoids the limitations of the prior art.
The need is met according to the present invention by providing a solid state area illumination light source that includes: a substrate; a plurality of non-pixellated organic light emitting diode (OLED) segments deposited on the substrate, each organic light emitting diode segment including a first and a second electrode for providing electrical power to the OLED segment; an encapsulating cover covering the OLED segments; and a plurality of conductors located on the substrate and electrically connected to the first and second electrodes, and extending beyond the encapsulating cover for making electrical contact to the first and second electrodes by an external power source.
The present invention has the advantage of providing an inexpensive, long lived, highly efficient light source for area illumination that can provide a variety of illumination levels, fails gracefully, and can provide a variety of colors.